<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>一个盒子</title>
    <style>
.box{
    width: 100px;
    height: 100px;
    background-color: royalblue;
    box-shadow: 10px 20px 10px sienna;
    /* 圆角 */
    border-radius: 10px 10px 10px 10px;
    float: left;
    
}
.box:hover{
    outline:10px black solid;
}
.box1{
    width: 200px;
    height: 200px;
    background-color: black;
    float: left;
}
    </style>
</head>
<body>
    <div class="box"></div>
    <div class="box1"></div>
    <div class="box3"></div>
</body>
</html>